Cancer is the second leading cause of death in the United States and accounts for the deaths of one of every four Americans. According to the American Cancer Society, 7.6 million people worldwide died of cancer in 2007.
Camptothecin is a well known anticancer drug isolated from the Chinese native tree Camptotheca acuminate. It is an optically active (20S) alkaloid of the fused ring system shown below.

Many efforts have been directed to synthesizing camptothecin derivatives to modify the cytotoxicity activity and/or improve water-solubility. Patent Corporation Treaty (PCT) International Application No. PCT/US95/08786 (WO 96/02546) discloses water-soluble esters of camptothecin compounds wherein the E-ring of the camptothecin esters has one of the structures shown below where m, R9, R10 and R11 have the definitions as given:

In addition, U.S. patent application Ser. No. 11/444,150 (U.S. 20070093432) discloses camptothecin-based compounds modified by positing at least one electron-affinic group around the camptothecin structure to enhance their value in combination with radiotherapy. Other camptothecin derivatives include, for example, topotecan, which is of the structure shown below.

A need continues to exist for new camptothecin derivatives with anticancer activities.